getting everyone in focus

[Derrel]

Learn how to hold in the depth of field preview, and how to focus "stopped down". Meaning, focusing manually, and placing the depth of field band visually, with the lens stopped down to shooting aperture. At close distances, focusing is of course absolutely CRITICAL. If there are two people and they are not very close to the same plane, then f/5.6 will not yield sufficient depth of field.

It's better to be a bit farther back if you insist on shooting at f/5.6...but the truth of the matter is f/8 to f/11 is a much better aperture for quick, run-n-gun type flash shooting...or even laid-back studio shooting or whatnot...the smaller apertures like f/8 to f/11 give a deeper depth of field band, which makes it easier to pose people in informal groups, without needing to direct people into poses so that their heads are all close to the same distance.

 

[SurvivalDad]

See, this is next level stuff. This is why I joined this forum. Time to learn.

 

[table1349]

Start here: Digital Photography Tutorials
Then read this: Strobist

 

[The_Traveler]

There seems to be a lot of things going on here.
You are shooting with a flash well below the needed synch speed and at an iso certainly well below what the 7100 sensor will give you without non-correctable noise.

Nikon D7100 Review - Hi iso nr
D7100 High iso samples 100 to 25600 Nikon DX SLR D40-D90 D3000-D7100 Talk Forum Digital Photography Review

You only have a couple of ways to fix this DOF problem - add more light so you can make the aperture smaller or increase the iso (and you have plenty of room there)

In regards the image itself, the background is getting a lot of light from the flashes and is bright thus competing for attention.
The man's bald head is actually shadowed and hurting the impression.